1. Field of the Disclosure
The present disclosure is generally directed to reciprocating pumps, and in particular, to systems, devices, and methods for mounting the fluid end assembly of a reciprocating pump to the power end of the pump.
2. Description of the Related Art
In many oilfield pumping applications, such as during water injection and/or formation fracturing operations, reciprocating pumps, such as plunger pumps and the like, are often called upon to deliver very high fluid discharge pressures. For example, the fluid discharge pressure in a typical formation fracturing operation is often in the range of approximately 70-100 MPa (10,000-15,000 psi) or even higher. Due to the operational characteristics of reciprocating pumps in general, the fluid end of the pump is subjected to high frequency cyclic pressure loading. In some extreme service pumps, such as those used for the high pressure oilfield applications noted above, very high stress intensities are frequently created along the inside surfaces of the fluid end pump housing. This is particularly the case in high stress concentration areas that occur at or near the structural discontinuities of the pump housing geometry, including the edges of the various intersecting bores passing through the housing, such as the plunger bore, suction and discharge bores, access bores, and the like.
Under the high magnitude cyclic stresses that are inherent in the high pressure pulsation loading of extreme service reciprocating plunger pumps, fatigue cracks will often develop in and around areas of high stress concentration in the fluid end pump housing, such as the various intersecting bore edges described above. Depending on the nature and extent of such fatigue cracking, it is often necessary to remove at least the fluid end of a high pressure reciprocating pump from service so that the fatigue cracks can be repaired, and/or so the pump housing can be replaced. Of course, during such repair and/or replacement activities the pump is not operating, a situation that increases both the time and overall cost of drilling operations. Therefore, in an effort to reduce pump downtime, different methods have been developed for mechanically connecting, the fluid end of a reciprocating pump to the power end. Accordingly, when repair and/or maintenance of the fluid end is required, the pump housing can be disconnected from the power end and replaced with a substantially identical pump housing unit, thus allowing pump operations to restart. FIGS. 1-3 illustrate some prior approaches that have been used for connecting the fluid end of a reciprocating plunger pump to the power end.
FIG. 1 is a partial cut-away perspective view of a prior art reciprocating pump 100 having a power end 110 for generating pumping power and a fluid end 120 for pumping fluid at a desired discharge pressure. The power end 110 is generally disposed inside of a frame or housing 111. The fluid end 120 includes a block or pump housing 121 through which a plurality of different intersecting bores pass, such as a plunger bore 137, a suction bore (not shown), a discharge bore 117, and an access bore 129. An inlet header 126 is connected to the pump housing 121 on the suction side of the fluid end 120, and an outlet nozzle 128 is connected to the housing 121 on the discharge side of the fluid end 120. The fluid end 120 also includes a plunger 124, which coupled to a plunger or pony rod 114 of the power end 110 and reciprocates inside of the plunger bore 137 during operation of the pump 100.
The fluid end 120 of the pump 100 is connected to the power end 110 by a plurality of tie rods 122, e.g., bolts, each of which passes through a spacer pipe or spacer tube 112. The spacer tubes 112 are used to provide a specified amount of standoff between fluid end 120 and the power end 110, generally based on the stroke length of the plunger 124. The tie rods 122 extend from the frame 111 of the power end 110 and pass completely through the pump housing 121—i.e., from the back side of the housing 121 to the front side—referred to here as a “through-bolted” mounting configuration. Each of the tie rods 122 are tightened by respective nuts 123, thus securing the fluid end 120 to the power end 110 with the spacer tubes 112 positioned therebetween.
In practice, when a typical through-bolted mounting configuration is employed, such as is shown for the pump 100 in FIG. 1, it can sometimes be very difficult to properly align the fluid end 120 and connect it to the power end 110. This can be further problematic as the total number of plungers 124 in the pump 100 increases, as there are more pump elements in general, and tie rods 122 in particular, to be aligned and connected. Accordingly, it can sometimes take several hours to remove a damaged or defective pump fluid end 120 from the power end 110 and re-connect a replacement fluid end 120. For example, in some applications it can take anywhere from approximately 2-6 hours to perform the required fluid end removal and replacement activities, particularly when unexpected problems arise. Additionally, in the through-bolted mounting configuration shown in FIG. 1, each of the tie rods 122 will act to resist the hydrostatic end loads that are imposed on the fluid end 120 during pump operation. As such, the tie rods 122 must generally be torqued to very high and precise pre-load levels in order to reduce the fatigue effects associated with the highly cyclic nature of the pump pressure loads, i.e., caused by the reciprocating action of plunger 124. However, even when such high pre-load levels are used, failure of the tie rods 122, such as cracking or breaking, can still occur, thus leading to additional pump down time so that failed and/or damaged tie rods 122 can be replaced.
FIG. 2 is a perspective view of another prior art reciprocating pump 200 that employs a different approach for mounting the fluid end 220 of the pump 200 to the power end 210. In some respects, the pump 200 is similarly configured to the pump 100, that is, the power end 210 is generally disposed inside of a frame or housing 211, and the fluid end 200 includes a block or pump housing 221. Additionally, an inlet header 226 is connected to the suction side of the pump housing 221 and an outlet nozzle 228 is connected to the fluid end 220 on the discharge side of the pump housing 221. The fluid end 220 also includes a plunger 224 that is coupled to a pony rod 224 on the power end 210 and which reciprocates inside of the plunger bore (not shown) during operation of the pump 200.
The fluid end 220 of the pump 200 is also connected to the power end 210 by a plurality of tie rods 222, each of which passes through a spacer tube 222 and is tightened by a nut 223. However, unlike the tie rods 122 of the pump 100 shown in FIG. 1, the tie rods 222 do not extend completely through the pump housing 221. Instead, the tie rods 222 connect the fluid end 220 of the pump 200 to the power end 210 by way of a bolted flange connection 230 that is mounted on the back side of the pump housing 221 generally referred to hereafter as a “flange bolted” mounting configuration. As shown in FIG. 2, the bolted flange connection 230 has an upper flange 225 that runs along substantially the entire length of the pump housing 221 (see, e.g., FIG. 3 described below) and a similarly configured lower flange 227 that is positioned on the opposite side of the pump plunger 224 from the upper flange 225. The tie rods 222 of the pump 200 therefore pass through holes in each of the respective upper and lower flanges 225, 227 but not through the entire pump housing 221.
FIG. 3 is a perspective view of a fluid end 320 of another prior art reciprocating pump 300, and illustrates a flange-bolted mounting configuration in greater detail. The fluid end 320 includes a pump housing 321 which has a fluid outlet 328 that is in fluid communication with each of the discharge side bores 317 of the fluid end 320. A bolted flange connection 330 is mounted on the back side of the pump housing 321 which, in the case of the fluid end 320 shown in FIG. 3, is sometimes formed as an integral part of the housing 321 by casting and/or machining.
Similar to the bolted flange connection 230 of the fluid end 220, the bolted flange connection 330 has an upper flange 325 and a lower flange 327, both of which extend along substantially the entire length of the pump housing 321. The upper flange 325 has a plurality of bolt holes 325h and the lower flange 327 has a plurality of boil holes 327 (one shown in FIG. 3) that correspond to each of the holes 325h. Furthermore, each of the bolts holes 325h and 327h receives a corresponding tie rod (not shown; see tie rods 222 in FIG. 2) that are used to connect the fluid end 320 of the pump 300 to the power end (not shown). The tie rods are then tightened using a plurality of nuts, such as the nuts 223 shown in FIG. 2.
In general, the flange-bolted mounting configurations shown in FIGS. 2 and 3 have at least some of the same alignment, assembly, and operational problems as are described with respect to the through-bolted mounting configuration show in FIG. 1. For example, the tie rods, such as the tie rods 222 shown in FIG. 2, must generally be torqued to very precise high pre-load levels in order to reduce the fatigue effects associated with the cyclic nature of the pump pressure loads. However, since there are typically more tie rods used for the flange-bolted mounting configurations than are used for the through-bolted mounting configurations, the tie rods used for the flange-bolted mounting configurations are sometimes smaller in diameter. In such cases, the required torque levels may be more easily achievable, thus incrementally reducing the amount of time needed to assemble the fluid end to the power end.
On the other hand, the upper and lower flanges that are used for the typical flange-bolted mounting configuration are generally subjected to a high degree of cyclic bending stresses, due at least in part to the pressure pulsations of the hydrostatic end load on the fluid end as caused by the reciprocating plunger, and the manner in which the upper and lower flanges are loaded during pump operation. When coupled with the stress concentrations at the structural discontinuities around the upper and lower flanges, these highly cyclic bending stresses can lead to the creation of additional fatigue cracks, thus potentially compounding the fatigue-related problems and/or failures that are so often associated with the intersecting edges of the various internal pump bores. Therefore, while the use of the flange-bolted mounting configuration may result in an incremental time savings when replacing a damaged fluid end, the frequency at which such flange-bolted mounting fluid end configurations must be replaced can be exacerbated by the cyclic bending stresses and additional stress concentration areas associated with the flange-bolted mounting configuration.
The present disclosure is directed to various new systems, devices, and methods that may reduce and/or mitigate at least some of the above-described problems that are associated with the prior art approaches for mounting a fluid end assembly of a reciprocating pump to the power end of the pump.